In the field of biochemistry, attention has been paid to techniques for separating, synthesizing, extracting or analyzing trace amounts of reagents using microreactors. The microreactor is composed of a microchip in which channels for microscale analysis and the like are formed on a small substrate formed of, for example, silicon, a silicone resin or glass by a semiconductor microfabrication technique.
A reaction analysis system using such a microreactor is called a micro total analysis system (hereinafter referred to as “μTAS”). According to the μTAS, since the ratio of the surface area to the volume of the reagent becomes large, a high-speed and high-precision reaction analysis can be performed and a compact automated system can also be realized.
In the microchip, a microchip suitable for various applications can be formed by providing a functional region having various functions such as a reaction region in which a reagent is disposed in a flow path called a microchannel. As applications of the microchip, may be mentioned analysis in the fields of chemistry, biochemistry, pharmacology, medicine, and veterinary medicine, such as gene analysis, clinical diagnosis, drug screening, and the like, and synthesis of compounds, environmental measurement, and the like.
In such a microchip, a pair of microchip substrates are typically bonded to each other so as to face each other, and a minute flow path having a width of, for example, 10 to several hundred μm and a depth of, for example, 10 to several hundred μm is formed in a surface of at least one of the microchip substrates. As the microchip substrate, a glass substrate is mainly adopted because it is easy to produce and optical detection is possible. Recently, development of a microchip using an inexpensive synthetic resin substrate, which is lighter in weight but harder to break than a glass substrate, has been promoted.
In the production of the microchip, as a method of bonding two microchip substrates to each other, a method of bonding with an adhesive, a method of thermal fusion bonding, or the like is conceivable.
However, these methods have the following problems. That is, in the method of bonding with an adhesive, there may be possible problems that the adhesive seeps into the minute flow path and so the flow path may be clogged, that part of the minute flow path may be narrowed and the diameter of the flow path may become uneven, and that disturbance may occur in the uniform characteristic on the wall surface of the flow path. In addition, in the method of bonding by thermal fusion, there may be problems that, if fusion bolding is performed at a temperature not lower than the heat melting temperature, the flow path may be crushed at the heating step, and that the flow path may not be maintained in a predetermined cross-sectional shape, and so it is difficult to sophisticate the functions of the microchip.
Therefore, there has been proposed a method of irradiating vacuum ultraviolet rays to each of the bonding surfaces of two substrates, or converting a process gas into plasma under atmospheric pressure or in the vicinity thereof and bringing the plasma-converted process gas into contact with the surface of the substrate, thereby activating the bonding surface of each substrate, and then stacking and bonding the two substrates so that the bonding surfaces are brought into contact with each other (see, for example, Patent Literature 1 to Patent Literature 5).
In addition, there has also been proposed a method of allowing a bonding film to be interposed between two substrates, and irradiating the bonding film with ultraviolet rays to develop adhesiveness of the bonding film, thereby bonding the two substrates by the adhesiveness (see, for example, Patent Literature 6).